A digital micromirror device (DMD) is a form of a micro-electrical mechanical system (MEMS) with a large number of micromirrors that individually pivot about an axis based upon the state of associated memory cells. For example, a micromirror may pivot to a first position if an associated memory cell contains a first value, and if the associated memory cell contains a second value, the micromirror may pivot to a second position.
A common use for a DMD is as an array of light modulators in an image display system, wherein the micromirrors in the DMD modulate light from a light source based on image data of an image being displayed. When a micromirror is in a first position, light from the light source reflects onto a display plane, while a micromirror in a second position reflects light away from the display plane. A combination of the micromirrors in the DMD operating in unison creates a projection of the image on the display plane.
In a typical DMD, a first position may correspond to micromirrors coming to rest at +18, +16, +14, +12, or so forth, degrees from a normal of the DMD's surface, and a second position may correspond to micromirrors coming to rest at −18, −16, −14, −12, or so on, degrees from the normal. For applications such as image display using non-coherent light for viewing purposes, a tight tolerance to the rest positions may not be required. Therefore, the tolerance may be as loose as +/− one (1) degree from the rest position.
However, for other applications that make use of a DMD, such a loose tolerance may not be acceptable. For example, in display systems that use laser illumination, a tight tolerance at the rest position of the micromirrors of the DMD may be needed to ensure that coherent light reflecting off the DMD enters a narrow iris and into an optical path of the display system. Similarly, in many emerging applications of DMDs, such as in short wavelength photolithography and holography, a tight tolerance on the rest positions of the micromirrors of the DMD may be required to ensure sharp images, good light intensity, and good depth of focus.